Failed to mount /system_root (Permission Denied), need help

[nanerbs25]

so my friend and i built a twrp tree for the Umidigi A7S with mt6737m with a kernel of 4.9.1, while it did booted, it cant update the partition /system_root, so no mount, so i tried to fix that and now, it errors "Failed to mount /system_root (Permission Denied)" same thing to vendor, and product partitions